FIG. 10 is a plan view showing a first conventional example of a semiconductor device. A semiconductor device 300 of the first conventional example is an LDO (Low Drop-Out) regulator IC which generates a desired output voltage Vo from an input voltage Vi by controlling conductivity of a power transistor 310 connected between an input terminal PIN11 and an output terminal PIN12. Further, the input terminal PIN11 and a pad 311 are bonded to each other through a wire W11 and the output terminal PIN12 and a pad 312 are bonded to each other through a wire W12.
FIG. 11 is a plan view showing a second conventional example of a semiconductor device. A semiconductor device 400 of the second conventional example is a switching regulator IC which outputs a rectangular waveform of switch voltage Vsw from a switch terminal PIN23 by turning on/off an upper power transistor 410H and a lower power transistor 410L connected in series between an input terminal PIN21 and a ground terminal PIN22. Further, the input terminal PIN21 and a pad 411 are bonded to each other through a wire W21, the ground terminal PIN22 and a pad 412 are bonded to each other through a wire W22, and the switch terminal PIN23 and a pad 413 are bonded to each other through a wire W23.
The power transistor 310 acts as a heat source when the semiconductor device 300 is operated, and the upper power transistor 410H and the lower power transistor 410L act as heat sources when the semiconductor device 400 is operated. On that account, the semiconductor devices 300 and 400 incorporate overheat protection circuits 320 and 420, respectively, which perform a protective operation when a junction temperature exceeds a threshold temperature.
In a conventional semiconductor device, sensitivity and accuracy of the overheat protection circuit were improved by reducing a distance between the heat source and the overheat protection circuit.
As shown in FIG. 10, however, if the size of the power transistor 310 acting as the heat source is large, there occurs an unavoidable temperature gradient between a portion HS which is the hottest portion within the power transistor 310 and an edge of the power transistor 310. This might make it impossible to perform correct heat detection even when the distance between the power transistor 310 and the overheat protection circuit 320 is somewhat reduced.
In addition, as shown in FIG. 11, when the upper power transistor 410H and the lower power transistor 410L acting as the heat sources are turned on/off, in order to prevent the overheat protection circuit 420 from malfunctioning due to switching noise, there is a need to keep a distance between the upper power transistor 410H and lower power transistor 410L and the overheat protection circuit 420 or provide a buffer zone 430 therebetween, which might result in reduced sensitivity and accuracy of the overheat protection circuit 420.
In addition, the conventional technique described above merely aimed at reducing a delay in a temperature transfer or an offset of a temperature detection value between discrete components (ranging from a power element (heat source) to a temperature sensor (heat detection part)) mounted on a circuit board (printed wiring board), rather than improving the sensitivity and accuracy of the overheat protection circuit integrated on the semiconductor device.